GROSS, J.B.*; HANKEN, J.; Museum of Comparative Zoology, Harvard University; Museum of Comparative Zoology, Harvard University: Embryonic origin of adult cranial cartilages in Xenopus: A view from the crest.

Characterizing the embryonic origin of the adult skull in frogs has long been problematic. This is due largely to the technical difficulty of following embryonic cells through and beyond metamorphosis. The origin of cranial cartilages is of particular interest since many structures are lost, remodeled or form initially as the tadpole metamorphoses to an adult. We traced long-term contributions of cranial neural crest to the adult skull in Xenopus laevis using a technique of chimeric grafting of transgenically labeled neural crest. The mandibular stream gives rise to �first arch� structures in the tadpole (e.g., Meckel�s and palatoquadrate cartilages). Similarly, these structures retain their cellular origins from the mandibular stream in the adult. Cells from the hyoid stream had an unexpected distribution in several adult cartilages, particularly in the nasal region, e.g., alary cartilages and nasal septum. Some portions of the nasal region, however demonstrated a �mixed� origin, receiving cells from both mandibular and hyoid streams. Interestingly, the branchial stream contributes minimally to cartilage in the post-metamorphic skull. The pattern of derivation in Xenopus differs markedly from those reported for other vertebrate models (chicken and mouse) suggesting the contribution of neural crest to adult cranial cartilages is more labile than previously revealed. The pattern in Xenopus may be a consequence of the evolution of metamorphosis in anurans having significantly altered the spatial distribution of these embryonic cells between early juvenile stages and adulthood. Supported by NSF EF-0334846 (AmphibiaTree) and the Milton Fund (Harvard University).